1. Field of the Invention
The present invention relates to a data driver of a flat panel display and a flat panel display including the data driver, and more particularly to a data driver for storing data and including a holding latch performing a function as a counter, and a flat panel display using the same.
2. Description of the Related Art
Recently, various flat plate displays capable of reducing weight and volume, which are disadvantages of cathode ray tubes (CRT), have been developed. Flat panel displays include liquid crystal displays (LCD), field emission displays (FED), plasma display panels (PDP), and organic light emitting displays.
Among the flat panel displays, a liquid crystal display displays images by controlling transmission of light generated from an external back light. Through development of the technology, a liquid crystal display with a large screen area having a high resolution has been developed, and accordingly has been used in various applications. An organic light emitting display displays images through an organic light emitting diode, which generates light by recombination processes of electrons and holes. Since the organic light emitting display has a fast response speed and is driven with low power consumption, it comes into the spotlight as the next generation display.
Each of the liquid crystal display and the organic light emitting display includes pixels, a data driver, and a scan driver. The pixels are defined at intersections of scan lines and data lines. The data driver is coupled to the data lines. The scan driver is coupled to the scan lines. The scan driver sequentially supplies a scan signal to the scan lines sequentially selecting pixels in a scan line. The data driver supplies a data signal to the data lines being synchronized with the scan signal. Accordingly, the data signal is supplied to pixels selected by the scan signal, and images of predetermined luminance are displayed according to the supplied data signal.
The data driver uses a digital-analog converter to convert external digital data into predetermined voltage levels, which can be referred to as a data signal. However, because the digital-analog converter includes a plurality of resistors and switches, it requires larger size and its manufacturing cost is high. In order to solve the problems, a method for generating a ramp pulse and supplying the ramp pulse to a data line at predetermined time as a data signal, has been suggested.
FIG. 1 is a diagram schematically showing a structure of a data driver for supplying a data signal using a ramp pulse. With reference to FIG. 1, the data driver includes a holding latch unit 10 and a data signal generator 20. The holding latch unit 10 stores data. The data signal generator 20 generates a data signal corresponding to the data stored in the holding latch unit 10. The holding latch unit 10 includes holding latches 12a, 12b, 12c, etc. for storing data supplied from an external apparatus, for example, a sampling latch unit. Each of the holding latches 12a, 12b, 12c, etc. forms an independent channel, stores data, and supplies the stored data to the data signal generator 20.
The data signal generator 20 includes counters 22a, 22b, 22c, etc., and first transistors M1a, M1b, M1c, etc. The counters 22a, 22b, 22c, etc. are disposed at separate channels. The first transistors M1a, M1b, M1c, etc. are coupled to the counters 22a, 22b, 22c, etc., respectively. Each of the counters 22a, 22b, 22c, etc. generates a counting signal, and provides the counting signal to the coupled first transistor. The start of the counting signal is synchronized with the start of the supply of the data to the counter. The counting signal is continuously generated for a time period that corresponds to the value of the data supplied to the counter. The generation of the counting signal stops after the time period determined by the value of the data.
When the counting signal is supplied, the first transistors M1a, M1b, M1c, etc. are turned on to provide a ramp pulse from an external apparatus to an output terminal OUT1 for a data signal. Because a stop time of the counting signal is determined by the value of the data, a data signal can be generated corresponding to the value of the data.
FIG. 2A shows graphs illustrating an operation of a first counter 22a, and FIG. 2B shows graphs illustrating an operation of a second counter 22b. With reference to FIG. 2A and FIG. 2B, the first counter 22a receives data of “00000100” (represented in a binary numeral system), and the second counter 22b receives data of “11010000.” When the first counter 22a receives data of “00000100”, it generates a counting signal counting from “00000000” to “00000100.” While the counting signal is supplied to the first-first transistor M1a, the transistor M1a is being turned on. If the supply of the counting signal stops, the first-first transistor M1a is turned off. A time period for turning on the first-first transistor M1a is determined by the value of the data supplied to the first counter 22a. Accordingly, through the ramp pulse, voltage levels corresponding to the value of the data is provided. A capacitor (not shown), which is connected to the transistor, holds the charges supplied during the time period for turning on the transistor, and outputs voltage for a data signal through its output terminal OUT. The capacitor can be a parasitic capacitor.
When the second counter 22b receives data of “11010000,” it generates a counting signal counting from “00000000” to “11010000.” While the counting signal is supplied to the second-first transistor M1b, the second-first transistor M1b is being turned on. If the supply of the counting signal stops, the second-first transistor M1b is turned off. A time period for turning on the second-first transistor M1b is determined by the value of the data supplied to the second counter 22b. Accordingly, through the ramp pulse, voltage levels corresponding to the value of the data is provided to the output terminal OUT as a data signal.
However, this data driver requires counters 22a, 22b, 22c, etc. for every channel, and therefore the circuit for the data driver is complicated, and a mounting area increases.